1. Technical Field
Example embodiments relate to a method of fabricating an image sensor, and more particularly, to a method of fabricating an image sensor having improved reliability.
2. Description of Related Art
Image sensors are devices that convert an optical image into an electrical signal. With recent developments in the computer industry and in the communication industry, a demand for CMOS image sensors having improved performance is increasing in various fields, e.g., digital cameras, camcorders, personal communication systems (PCSs), game players, security cameras, medical micro cameras, and robots.
Each unit pixel of an image sensor includes a photoelectric conversion unit and a charge transmission unit which transmits electric charges generated by photoelectric conversion performed on incident light in the photoelectric conversion unit to a charge detection unit.
In a process for manufacturing an image sensor, etching and/or ion implementation may be repeated. Silicon and oxygen may combine on the surface of a semiconductor substrate, causing damage to the substrate, resulting in a dangling bond, e.g., (—Si—O—) and/or (—Si—). The dangling bond deteriorates a dark current which flows from the photoelectric conversion unit to the charge transmission unit, thereby degrading the reliability of the image sensor. To remove this dangling bond, a method of radiating ultraviolet (UV) rays onto the semiconductor substrate or diffusing hydrogen may be used.
The image sensor includes an active pixel region and an optical black region. The active pixel region receives incident light and converts the incident light into an electrical signal. The optical black region blocks inflow of light and thus provides a reference of a black signal to the active pixel region.
In the optical black region of the image sensor, a light-blocking pattern for blocking light inflow is formed. The light-blocking pattern does not only block light inflow but also blocks UV or hydrogen from moving to the semiconductor substrate during a UV or hydrogen annealing process for removing a dangling bond.
In other words, in the active pixel region of the image sensor, the dangling bond is removed using UV or hydrogen. On the other hand, in the optical black region of the image sensor, diffusion of UV or hydrogen is prevented or reduced by the light-blocking pattern, and thus, the dangling bond is not removed. Therefore, signals represented in the active pixel region and the optical black region of the image sensor are different, causing degradation of the reliability of the image sensor.